The problem of forming an end face wall having a concentric recess in a tubular workpiece arose due to the necessity of considerably increasing the efficiency of manufacturing the bodies of belt conveyor rollers.
According to conventional methods, such bodies have been made of a case and inserts placed into the case and joined by welding or rolling-in therewith. Such methods are labour-consuming, low efficient and metal-wasting.
Making such bodies all-in-one by casting would only increase these disadvantages adding such ones as the limited choice in metal and dimensions of bodies and would also increase the amount of machining them.
The problem of forming all-in-one bodies of conveyor rollers in connection with known in the art methods of metal working may be taken as a general problem of forming a face wall having a concentric recess in a hollow cylindrical article.
Known in the art is a method of forming a recess in the bottom of a cylindrical body by reverse drawing (see V. P. Romanovsky, "Spravochnik po knolodnoy shtampovke" /Cold Stamping Handlbook/, 6th edition, 1979, Leningrad, "Mashinostroenie" Publishing House, pp. 128-129) comprising locating the body in a female die having an internal opening concentrical to the outer surface which is smoothly conjugated with the wall of the opening, and pressing the bottom into the opening of the female die by a male die. This results in bending the metal of the body according to the radius of the female die surfaces conjugation and thus in the formation of a concentric recess in the bottom.
The above method cannot be utilized for the production of all-in-one bodies of conveyor rollers because by this method a face wall having a recess may be obtained only at one end of a hollow cylindrical workpiece while the other end thereof is open. Moreover, a recess obtained by this method has a limited range of diameters which are dependent on the reduction ratio of the material.
The problem under consideration may be solved, for example, by unrestrictedly reversing a tubular workpiece end inwardly.
One of the methods utilizing such reversing consists in upsetting a tubular workpiece end in a die designed for the purpose by axially motioning the tubular workpiece while heating the metal of the workpiece in the area of deformation. This results in bending the wall of the workpiece according to a radius of free bend inside the tubular workpiece and moving the metal of the bent edge thereof in the direction opposite to motion of the remaining portion of the workpiece.
An internal neck is obtained in the workpiece, which neck is conjugated with the side wall of the workpiece by means of an end face having a toroidal surface (see O. V. Popov, "Izgotovlenie Tselnoshtampovannykh Tonkostennykh Detaley Peremennogo secheniya" /Production of All-Stamped Thin-Walled Parts of Variable Sections/, 1974, Moscow, Mashinostroenie" Publishing House, p.p. 57-62).
Necks of only a definite diameter depending on the external diameter of a workpiece may be obtained by the above method in thin-walled tubular workpieces because under other conditions the method is unstable. Moreover, the shape of the end face wall of the workpiece cannot be another than toroidal. Besides, the efficiency of the method is decreased by the necessity of heating in the area of deformation.
The abovementioned disadvantages of the prior art methods of stamping on one hand, and the equipment simplicity and high efficiency of prior art methods of rolling on the other hand helped the workers in the art to adhere to the latter methods in searching for the ways of manufacturing all-in-one bodies of conveyor rollers.
Known in said field is a method of forming in a cylindrical article an end face wall having a concentric recess of any predetermined size and shape by sequentially rolling, first, the recess and, then, the end face wall and the side wall of the article from a sheet round stock (see V. G. Kaporovich, "Obkatka v proizvodstve metalloizdeliy" /Rolling in Metal Products Manufacturing/, 1973, Moscow, "Mashinostroenie" Publishing House, p. 97).
However, this method is suitable only for forming hollow cylindrical articles having an open end and the diameter which is commensurable with the length thereof while said bodies comprise the aforementioned end face walls having recesses at both ends thereof and their length is several times the diameter thereof.
Known in the art is a method of forming an end face wall having a concentric recess in a tubular workpiece, which is a step in a process of manufacturing a steel flask (see V. G. Kaporovich, "Proizvodstvo detaley iz trub obkatkoy" /Production of Parts from Tubing by Rolling/, 1978, Moscow, "Mashinostroenie" Publishing House, p.p. 129, 67-69, 16-17). The method comprises deforming a side wall of a workpiece at an end thereof in the direction of closing the workpiece end edges to the formation of a vault, forming a face wall from the obtained vault, and reversing said end of the rotated workpiece inwardly at a forging temperature. Deforming the side wall and forming the face wall is performed sequentially by means of different tools for rolling fixed, in this case, in a single holder. Reversing the end inwardly is performed by the method of U.S. Pat. No. 2,449,247, Cl. 72-69, 1948, comprising axially feeding a tool of a special design being rotated about its axis. The tool comprises a body provided with a central bore and an inward projection at the bottom thereof. Three U-shaped pins of a wear-resistant material are pressure-fitted into said bore so that each of them follows the side wall, a part of the bottom and the projection and protrudes from the internal surface of the body at 0.20-0.35 of the pin's diameter. In the process of axially feeding, the end of the workpiece is heated up to a forging temperature. The side wall of the workpiece serves as a guide in the axial motion of the tool whose projection presses through the preformed face wall inwardly. The recess formed in the end face wall of the workpiece opens up thus forming a through neck due to the pressure of the tool projection.
Forming the shape of the tubular workpiece by reversing is possible only after the radius which is equal to or less than a free bend radius (see O. V. Popov, "Izgotovlenie tselnoshtampovannyh tonkostennyh detaley peremennogo sechenia" /Production of All-Stamped Thin-Walled Parts of Variable Sections/, 1974, Moscow, "Mashinostroenie" Publishing House, p.p. 57-58). That is why by this method may be obtained an internal neck the diameter of which cannot be less than D.sub.e -4R, where D.sub.e is the external diameter of the tubular workpiece portion to be deformed and R is a radius of free bend which is quite a definite value for any tubular workpiece and depends upon the diameter and the wall thickness thereof. The internal neck is conjugated with the side wall of the workpiece by means of the end face wall, which cannot be other than toroidal-shaped (circumscribed by said radius). An additional step is required to form the end face wall of other shape.
To disadvantages of the described method may also be related the fact that the reversing operation may proceed steadily only with tubes whose diameter is up to 50 mm and a relative wall thickness ((t/D.sub.e)=100%, where t is the wall thickness) is not more than 3.5%. Exceeding said limits leads to considerably thickening the wall in the area of deformation, which hampers steady proceeding of the operation.
Thus, the performance capabilities of the described method are limited in both the choice in the initial dimensions of the workpiece and in the dimensions and the shapes of the end face walls and necks (recesses) to be formed.